The invention relates to a transmitter, a receiver and a method in a telecommunication system for providing PN sequences for different user channels. In particular, the present invention relates to such a transmitter, receiver and method in a telecommunication system, in which a plurality of user channels are processed using a time-slot multiplexing of user data in respective transmission frames.
Such PN sequences are generally used for performing bit error rate measurements in telecommunication systems. For this purpose, a known PN sequence of a predetermined length, i.e. a predetermined number of bits 2Nxe2x88x921 (where N denotes the number of shift registers of the PN generator) is encoded in the transmitter and the received sequence is decoded in the receiver.
FIG. 1 shows a general overview of a typical decoder circuit in a CDMA-system, where the block xe2x80x9cBER measurement {circle around (3)} xe2x80x9devaluates the bit error rate BER by decoding a received PN-sequence (PN: Pseudo noise). FIG. 2 shows the principle of performing such bit error rate measurement. A telecommunication system TELE comprises a transmitter TX and a receiver RX. In the transmitter TX a transmitter PN-generator T-PN (consisting of interconnected shift registers) is initialized with a predetermined sequence xe2x80x9c111111111xe2x80x9d and likewise at the receiver RX a PN-generator R-PN must be initialized with the same initializing sequence. It is essential, that the PN-generator T-PN in the transmitter TX and the PN-generator in the receiver RX are synchronized. As indicated in FIG. 2, one possibility is to use a control channel for setting the start timing of the PN-generators in the transmitter TX and in the receiver RX. Once the PN-generators have been initialized and started in the synchronized manner, the bit error rate measurement circuit in the receiver RX can compare the PN-sequence generated in the receiver with the received and decoded sequence from the transmitter TX in order to evaluate the discrepancies of the generated bits.
With respect to the PN-generators T-PN, R-PN, it may be noted that these PN-generators are generally constituted by a series connection of shift registers SH1-SHN with intermediate EXOR gates EX1-EXNxe2x88x921 (where EX1 denotes the first XOR gate and EXNxe2x88x921 denotes the (Nxe2x88x921)th XOR gate, i.e. the last provided XOR gate) from which the input of the first shift register SH1 of the PN-generator is built. This is a generally known configuration and an illustration of the general interconnection of the EXOR gates and the shift registers can be seen in FIG. 4. That is, the actual length 2Nxe2x88x921 of the PN-sequence is determined by the number N of shift registers and the actual polynomial used for generating the PN sequence, i.e. the type of the PN-sequence is determined by the number of inputs to the EXOR gates for the first shift register, as is well-known.
Thus, both transmitter and receiver PN-generators T-PN, R-PN of the telecommunication system TELE in FIG. 2 comprise such an interconnection of gates and shift registers and whenever user data of the user channel is to be coded by using the PN-sequence in a transmitter and using the PN-sequence in the receiver, the shift registers must be set with a predetermined sequence in a synchronized manner (where the bit sequence must not be a state of xe2x80x9call 0xe2x80x9d).
Whilst the general technique of performing bit error rate measurements using known PN-sequences and the constitution of the PN-generators as explained above is well-known in the prior art in order to evaluate one channel for one user, there are specific problems when time-slotted transmissions, i.e. time-slot multiplexing of user data on a plurality of user channels in respective transmission frames are used for the transmission between the transmitter TX and the receiver RX and/or for the processing of a plurality of user channels.
That is, FIG. 2 only shows the situation for performing bit error rate measurements for one user channel and if there are a plurality of users (user channels) which use one frame in a time-slotted manner, then invariably several PN-generators must be used, each dedicated to one user channel. That is, assuming that in a telecommunication system, where communications and/or processings are carried out using such a time-slot multiplexing technique, for example up to 512 user channels (depending on the channel size) can be handled and thus 512 individual channel bit error rate measurements must be performed by respectively using their specifically dedicated PN-sequences.
In this connection, it should be noted that the expression xe2x80x9ctime-slot multiplexing of user data on a plurality of user channels in respective transmission framesxe2x80x9d can relate to various different modulation schemes used in common telecommunication systems, i.e. TDMA multiplexing schemes or CDMA multiplexing schemes. The essential feature that is common to all such modulation schemes is that each user channel will be assigned a particular time-slot in a transmission frame. For example, FIG. 1 shows the general overview over a CDMA system, where a number of user channels are input to a slot demultiplexer and a decoding is carried out in the time-slot segmentation, the bit interleaving and the Viterbi decoder, before the user data undergoes the bit error rate measurement in the block {circle around (3)}. Here, in this CDMA system, for example up to 512 user channels are received in individual bursts in associated time-slots of a transmission frame.
In FIG. 3 two transmission frames FR of a time-slot mulitplexing system are shown. In each frame FR a great plurality of user channels (e.g. 512 user channels) must be accommodated. The complete user data of one user channel is distributed over a number of consecutive frames FR respectively at the same position (here at the beginning of the frame). However, the user data may also be distributed at different positions within the frame FR.
In FIG. 3 the user channel of user 1 is allocated to the first time-slot position in the frame FR. Typically with a frame length of 10 ms, a slot of 1/512 of the frame and a bit period of 8 MHz, only about 100 bits of the complete PN-sequence generated by the transmitter or receiver PN-generator can be accommodated in the first time-slot (user channel) in the first frame FR, as illustrated in FIG. 3. Of course, assuming for example N=9 shift registers in the PN-generator, the actual length of the Pseudo Noise sequence is 2Nxe2x88x921=511 bits. Therefore, of course only 100 bits are not sufficient in order to fully evaluate the channel for the user 1. Therefore, assuming that the PN-generators in the transmitter and in the receiver were synchronized at the beginning of the first frame, then the bit error rate measurement can not be continuously performed for the user 1, since only after a certain number of bits, i.e. 100 bits, the transmission is interruptedxe2x80x94for that userxe2x80x94within each frame. That is, after the first 100 bits of the first user channel 1, the next 100 bits of user channel 2 are transmitted, that is, the other positions in the first frame FR are respectively allocated to the other users. Therefore, between the start timing and the end timing of each time-slot only a limited number of bits from the PN-sequence used for the user channel 1 can be evaluated.
The consequence of this is that the PN-generators must stop their operationxe2x80x94for the first userxe2x80x94at the end timing of each time-slot at the receiver and the transmitter and must continue their PN-sequence generation from the last state (i.e. from a last phase state of the PN-generators) at the start timing of the respective time slot in the next frame (i.e. in FIG. 3 in the second frame FR). In particular, it is not possible to just let the PN-generator continue to output the bits of the bit sequence, when the next user channel starts, since the phase state, which the PN-generator had at the end timing of the first user time-slot, must be available, when the next portion of the user data of user channel 1 is transmitted at the first position in the second frame FR. That is, in the second frame the PN-generation must be continued from the last phase state which the PN-generator had at the end timing of the first time-slot in the first frame FR.
Therefore, as is shown in FIG. 4, each user channel 1, 2 . . . 512 is conventionally provided with separate PN-generators, whose operation is interrupted at the end timing of a number of bits corresponding to the available time-slot in the frame for each user. That is, the shift registers SH1 . . . SH9 schematically shown in FIG. 4 respectively generate the PN-sequence, however, they hold their internal phase state (defined as the bit sequence respectively stored in said shift registers) at the end timing of the respective time-slot, since they are simply stopped. Thus, a control means initiates the further generation of the bit sequence by triggering the respective PN-generator in accordance with the time-slot (user channel) at each slot position beginning in the frame.
The conventional solution shown in FIG. 4 has drastic disadvantage. For example, as was discussed with reference to the encoder circuit in FIG. 1, up to 512 different users may be present and thus up to 512 different PN-generators each to be initialized with 9 bits must be provided. Often such PN-generators are implemented in hardware using a FPGA (Field Programmable Gate Array) library, which can for example realize 4 flip-flops in 1 PFU (Programmable Functional Unit). In this case, the total amount mpFu of PFUs would be:
mpFu=512 (number of users) * 9 bit (number of shift registers N)=512 * 3 PFUs=1536 PFUs.
Besides the fact that no driving or control logic is included in the above calculation of mpFu for the required hardware, the individual PN-generators must be triggered at the correct time-slot position within the frame. Thus, the amount of hardware, i.e. 1536 PFUs, is very large in order to handle the bit error rate measurement for a large number of users such as are typically present in a CDMA system as is schematically shown in FIG. 1.
Above it has been explained that in particular for telecommunication systems using a time-slot multiplexing in frames for the processing of user channels, for example in the TDMA or CDMA transmission methods (CDMA uses a burst transmission) a number of user channels are employed and the problem exists that each user channel must perform its own BER measurement by employing a separate PN-generator in the transmitter and in the receiver which causes the high hardware amount.
Therefore, the object of the present invention is the provision of a transmitter, a receiver, a telecommunication system and a method, which allow the BER measurement for a plurality of user channels with minimum hardware resources
The object of the present invention is solved by a transmitter (claim 1) of a telecommunication system in which a plurality of user channels are processed using a time-slot multiplexing of user data in respective transmission frames, comprising one single transmitter PN generator including a number N of shift registers for generating PN sequences of a predetermined number of bits, wherein said predetermined number of bits 2Nxe2x88x921 is larger than the number of bits which can be transmitted for each user channel in a respective time slot, a PN generator phase state memory for storing phase states of said PN generator for each user channel, a phase state being defined as a bit sequence respectively stored in said shift registers of said PN generator, a timing means for detecting a start timing and an end timing of each time slot of each user channel and a read/write means for writing phase states read out from said memory into said PN generator and for writing phase states read out from said PN generator to said memory, said read/write means being adapted for reading out a phase state for a particular user channel from said memory and writing said read out phase state into said PN generator, when said timing means detects a start timing of a time slot in said frames assigned to said particular user channel, and for reading out the phase state of said PN generator and writing said read out phase state into said memory, when said timing means detects the end of the time slot belonging to said particular user channel.
Furthermore, this object is solved by a receiver (claim 9) of a telecommunication system in which a plurality of user channels are processed using a time-slot multiplexing of user data in respective transmission frames, comprising one single receiver PN generator including a number N of shift registers for generating PN sequences of a predetermined number of bits 2Nxe2x88x921, wherein said predetermined number of bits 2Nxe2x88x921 is larger than the number of bits which can be transmitted for each user channel in a respective time slot, a PN generator phase state memory for storing phase states of said PN generator for each user channel, a phase state being defined as a N bit sequence respectively stored in said shift registers of said PN generator, a timing means for detecting a start timing and an end timing of each time slot of each user channel, and a read/write means for writing phase states read out from said memory into said PN generator and for writing phase states read out from said PN generator to said memory, and said read/write means being adapted for reading out a phase state for a particular user channel from said memory and writing said read out phase state into said PN generator, when said timing means detects a start timing of a time slot in said frames assigned to said particular user channel, and for reading out the phase state of said PN generator and writing said read out phase state into said memory, when said timing means detects the end of the time slot belonging to said particular user channel.
Furthermore, this object is solved by a telecommunication system (claim 17) in which a plurality of user channels are processed using a time-slot multiplexing of user data in respective transmission frames, comprising at least one transmitter including a single transmitter PN generator including a number N of shift registers for generating PN sequences of a predetermined number of bits 2Nxe2x88x921, wherein said predetermined number of bits 2Nxe2x88x921 is larger than the number of bits which can be transmitted for each user channel in a respective time slot, a transmitter PN generator phase state memory for storing phase states of said transmitter PN generator for each user channel, a phase state being defined as a bit sequence respectively stored in said shift registers of said transmitter PN generator, a transmitter timing means for detecting a start timing and an end timing of each time slot of each user channel, a transmitter read/write means for writing phase states read out from said transmitter memory into said transmitter PN generator and for writing phase states read out from said transmitter PN generator to said transmitter memory, and said transmitter read/write means reading out a phase state of a particular user channel from said transmitter memory and writing said read out phase state into said transmitter PN generator, when said transmitter timing means detects a start timing a time slot in said frames assinged to said particular user channel, and reading out the phase state of said transmitter PN generator and writing said read out phase state into said transmitter memory, when said transmitter timing means detects the end timing of the time slot belonging to said particular user channel; and at least one receiver comprising one single receiver PN generator including a number N of shift registers for generating PN sequences of a predetermined number of bits 2Nxe2x88x921, wherein said predetermined number of bits 2Nxe2x88x921 is larger than the number of bits which can be transmitted for each user channel in a respective time slot, a receiver PN generator phase state memory for storing phase states of said receiver PN generator for each user channel, a phase state being defined as a N bit sequence respectively stored in said shift registers of said receiver PN generator, a receiver timing means for detecting a start timing and an end timing of each time slot of each user channel, a receiver read/write means for writing phase states read out from said receiver memory into said receiver PN generator and for writing phase states read out from said receiver PN generator to said receiver memory; and said receiver read/write means reading out a phase state of a particular user channel from said receiver memory and writing said read out phase state into said receiver PN generator, when said receiver timing means detects a start timing a time slot in said frames assinged to said particular user channel, and reading out the phase state of said receiver PN generator and writing said read out phase state into said receiver memory, when said receiver timing means detects the end of the time slot belonging to said particular user channel.
The object is also solved by a method (claim 26) for generating PN sequences of a predetermined number 2Nxe2x88x921 of bits for a plurality of user channels in a telecommunication system, in which said plurality of user channels are processed using a time-slot multiplexing of user data in respective transmission frames, by means of a single PN generator including a number N shift registers, wherein said predetermined number of bits of said PN sequence is larger than the number of bits which can be transmitted for each user channel in a respective time slot, comprising the steps of loading a PN generator with a user channel specific phase state stored in a PN generator phase state memory when a start timing of the time slot assigned to the specific user channel in the frame is detected, said phase state being defined as a N bit sequence, building the PN sequence for the specific user channel during the specific time slot, and writing the phase state obtained in said PN generator at the end of said specific time-slot into said PN generator phase state memory as a new user channel specific phase state, wherein said sequence of said loading, building and writing steps is repeated for each specific user channel in its specific time slot.
The object is also solved by a transmitter further comprising first inverters for inverting bits at predetermined bit positions of said phase state read out from the phase state memory before it is written into the PN generator and second inverters for inverting bits at said predetermined bit positions of the phase state PST read out from the PN generator before it is written into said phase state memory; a transmitter of a telecommunication system in which a plurality of user channels are processed using a time-slot multiplexing of user data in respective transmission frames, comprising: said PN sequence programming means comprises an address conversion means for converting a user channel address into programming signals and a gate means for receiving said programming signals and for feeding the output signals of said PN registers back via gates generating the input for the first shift register of said PN generator in response to said programming signal; said gate means includes a number of AND gates receiving said programming signal at one input and receiving said output signals of the shift registers at another input thereof and outputting a signal to a respective EXOR gate, said programming signal determining the type of PN sequence generated by said PN generator; said gate means further includes multiplexer gates having an output terminal connected to an input of the next shift registers, having one input terminal thereof connected to the output of the associated shift register and having another input terminal connected to the input of said associated shift register, and having a control input terminal connected for receiving a programming signal from said address conversion means, said programming signal applied to said multiplexer gates determining the length of PN sequence generated by said PN generator for each user channel.
The object is also solved by a receiver further comprising first inverters for inverting bits at predetermined bit positions of said phase state read out from the phase state memory before it is written into the PN generator and second inverters for inverting bits at said predetermined bit positions of the phase state read out from the PN generator before it is written into said phase state memory; a receiver of a telecommunication system in which a plurality of user channels are processed using a time-slot multiplexing of user data in respective transmission frames, comprising: one single receiver PN generator including a number of shift registers for generating PN sequences of a predetermined number of bits 2Nxe2x88x921, wherein said predetermined number of bits 2Nxe2x88x921 is larger than the number of bits which can be transmitted for each user channel in a respective time slot; a PN generator phase state memory for storing phase states of said PN generator for each user channel, a phase state being defined as a bit sequence respectively stored in said shift registers of said PN generator; a timing means for detecting a start timing and an end timing of each time slot of each user channel; a read/write means for writing phase states read out from said memory into said PN generator and for writing phase states read out from said PN generator to said memory; and said read/write means reading out a phase state for a particular user channel from said memory and writing said read out phase state into said PN generator, when said timing means detects a start timing of a time slot in said frames assigned to said particular user channel; and reading out the phase state of said PN generator and writing said read out phase state into said memory, when said timing means detects the end of the time slot belonging to said particular user channel; said PN generator comprises a sequence programming means for programming said PN generator to produce a predetermined PN sequence; said PN sequence programming means comprises an address conversion means for converting a user channel address into programming signals and a EXOR gate means for receiving said programming signals and for feeding the output signals of said shift registers back via EXOR gates generating the input for the first shift register of said PN generator in response to said programming signal; said gate means includes a number of AND gates receiving said programming signal at one input and receiving said output signals of the shift registers at another input thereof and outputting a signal to a respective EXOR gate, said programming signal determining the type of PN sequence generated by said PN generator; said gate means further includes multiplexer gates having an output terminal connected to an input of next shift register, having one input terminal thereof connected to the output of the associated shift register and having another input terminal connected to the input of said associated shift register and having a control input terminal connected for receiving a programming signal from said address conversion means, said programming signal applied to said multiplexer gates determining the length of the PN sequence generated by said PN generator for each user channel.
The object is also solved by a system wherein bits at predetermined bit positions of said phase state read out from the phase state memory are inverted before they are written into the PN generator and bits at said predetermined bit positions of the phase state read out from the generator are inverted before they are written into said phase state memory; a telecommunication system in which a plurality of user channels are processed using a time-slot multiplexing of user data in respective transmission frames, comprising at least one transmitter, comprising: one single transmitter generator including a number of shift registers for generating sequences of a predetermined number of bits (2Nxe2x88x921), wherein said predetermined number of number of bits (2Nxe2x88x921) is larger than the number of bits which can be transmitted for each user channel in a respective time slot; a transmitter PN generator phase state memory for storing phase states of said transmitter PN generator for each user channel, a phase state being defined as a bit sequence respectively stored in said shift registers of said transmitter generator; a transmitter timing means for detecting a start timing and an end timing of each time slot of each user channel; a transmitter read/write means for writing phase states read out from said transmitter memory into said transmitter generator and for writing phase states read out from said transmitter generator to said transmitter memory; and said transmitter read/write means; reading out a phase state of a particular user channel from said transmitter memory and writing said read out phase state into said transmitter generator, when said transmitter timing means detects a start timing a time slot in said frames assinged to said particular user channel; and reading out the phase state of said transmitter PN generator and writing said read out phase state into said transmitter memory, when said transmitter timing means detects the end of the time slot belonging to said particular user channel; and at least one receiver, comprising: one single receiver PN generator including a number of shift registers for generating PN sequences of a predetermined number of bits (2Nxe2x88x921), wherein said predetermined number of bits (2Nxe2x88x921) is larger than the number of bits which can be transmitted for each user channel in a respective time slot; a receiver PN generator phase state memory for storing phase states of said receiver PN generator for each user channel, a phase state being defined as a N bit sequence respectively stored in said shift registers of said receiver PN generator; a receiver timing means for detecting a start timing and an end timing of each time slot of each user channel; a receiver read/write means for writing phase states read out from said receiver memory into said receiver PN generator and for writing phase states read out from said receiver PN generator to said receiver memory; and said receiver read/write means; reading out a phase state of a particular user channel from said receiver memory and writing said read out phase state into said receiver PN generator, when said receiver timing means detects a start timing a time slot in said frames assinged to said particular user channel; and reading out the phase state of said receiver PN generator and writing said read out phase state into said receiver memory, when said receiver timing means detects the end of the time slot belonging to said particular user channel; said PN generators comprise respectively a PN sequence programming means for programming said PN generator to produce a predetermined PN sequence; said PN sequence programming means comprises an address conversion means for converting a user channel address into programming signals and a gate means for receiving said programming signals and for feeding the output signals of said shift registers back via EXOR gates generating the input for the first shift register of said PN generator in response to said programming signal; said gate means includes a number of AND gates receiving said programming signal at one input and receiving said output signals of the shift registers at another input thereof and outputting a signal to a respective EXOR gate, said programming signal determining the type of PN sequence generated by said PN generator; said gate means further includes multiplexer gates having an output terminal connected to an input of the next shift register, having one input terminal thereof connected to the ouptut of the associated shift register and having another input terminal connected to the input of said associated shift register and having a control terminal connected for receiving a programming signal from said address conversion means, said programming signal applied to said multiplexer gates determining the length of PN sequence generated by said PN generator for each user channel.
According to one aspect of the invention only a single PN-generator in the transmitter and in the receiver is necessary. Instead of using a plurality of PN-generators in the transmitter and in the receiver, the invention uses a state memory, in which the intermediate states (phase states) of each PN-sequence for each channel are stored. If the correct start timing (correct position) in the frame arrives for the respective user channel, the corresponding last phase state of the PN-generator is read from the state memory (RAM) and is used for a re-initialization of the PN-generator at the re-start of the corresponding time-slot of the next frame. As will be explained below the usage of only one PN-generator and one state memory drastically reduces the hardware amount necessary.
According to another aspect of the invention, each user channel can use a different PN-sequence, since the PN-generator can be programmed to yield different PN-sequences in response to a programming signal. That is, if for example there are different kinds of user data in different user channels, the length and the polynomial of the PN-sequence can be different for each user channel. This is advantageously achieved by not only using the read-out address for reading out the last bit sequence from the state memory but by also using it for addressing a PN-sequence programming means of the PN-generator, which in accordance to a programming signal will generate different types and lengths of PN-sequences.
Further advantageous embodiments and improvements of the invention are listed in the dependent claims. Hereinafter, the invention will be explained with reference to its embodiments.